1. Field of the Invention
The present invention relates to a cooling system and cooling method for the hot isostatic pressurizing (HIP) equipment.
2. Description of the Prior Art
One of the disadvantages of HIP processing is the lengthy cycle time. One way to reduce the cycle time is to shorten the cooling time after heating as far as possible. This is usually accomplished by rapidly cooling the hot gas used for heating. The cooling method involves releasing the hot gas from the heat-insulated furnace through a vent hole formed in the top of the heat insulator, introducing the released hot gas into a high-pressure chamber, and causing the hot gas to circulate therein by forced or natural convection so that the hot gas undergoes heat exchange with the high-pressure vessel and top closure.
A cooling system for this method is disclosed in Japanese Utility Model Laid-open No. 123999/1988. It comprises a stirring fan for uniform cooling in the furnace and an inner bottom closure which can be removed downward together with a processed workpiece placed thereon, with the heater remaining in the vessel. This arrangement facilitates the handling of the workpiece.
A disadvantage of this prior art technology is that the valve to release hot gas is subject to damage due to thermal deformation because it is attached to the top of the heat insulator and hence is exposed to hot gas. Another disadvantage is that the heat insulator is deformed by the axial force which is applied as the valve is actuated, because the axial force of the actuator is supported by the heat insulator.
A device to overcome these disadvantages is disclosed in Japanese Patent Laid-open No. 87032/1984. It comprises a damper ring which is attached to the lower part of the furnace to avoid the effect of hot gas. A disadvantage of this device is that the damper (including the actuator) needs a large space for its accommodation which makes it necessary to increase the diameter of the vessel. This disadvantage is economically serious in the case of HIP equipment designed for high pressure in excess of 100 MPa.